A. Field of the Invention
This invention relates generally to the fields of dentistry and orthodontics. More particularly, the invention relates to methods and apparatus for registering an object of known predetermined geometry to scanned three dimensional data such that the object's location in space may be verified. Such a known object may comprise a three-dimensional (3-D) digital object such as a virtual dental appliance (e.g., a virtual tooth bracket) or other like object. Knowledge of such an object's location is generally helpful in planning orthodontic treatment, particularly where the location of the appliance needs to be determined or confirmed or where incomplete or poor scan data is obtained. Aspects of the present invention provide methods of effectively verifying bracket location and displaying bracket locations using a computer and three-dimensional virtual models of teeth.
B. Description of Related Art
In orthodontics, a patient suffering from a malocclusion is typically treated by bonding brackets to the surface of the patient's teeth. The brackets have slots for receiving an archwire. The bracket-archwire interaction governs forces applied to the teeth and defines the desired direction of tooth movement. Typically, the bends in the wire are made manually by the orthodontist. During the course of treatment, the movement of the teeth is monitored so as to track the movement of the teeth. Corrections to bracket positions and/or wire shape can made manually by the orthodontist.
One key efficiency in treatment and maximum quality in results is a realistic simulation of the treatment process. Today's orthodontists have the possibility of taking plaster models of the upper and lower jaw, cutting the model into single tooth models and sticking these tooth models into a wax bed, and lining them up in the desired position. This approach allows for reaching a desired occlusion while minimizing guess work. A next step is bonding a bracket at every tooth model. This would tell the orthodontist the geometry of the wire to run through the bracket slots to receive a desired result.
Different types of bracket bonding methods may be implemented. In a first method, a bracket placement tray is used. In the bracket placement tray method, a placement tray is utilized to bond the various brackets to the tooth. With the bracket placement tray method, the general location of bracket placement is known. Each bracket and bracket location can be stored in memory for future retrieval.
Alternatively, a more traditional manual method may be used where the treating physician manually bonds a bracket to each tooth. In such a manual process, the actual bracket placement is not generally known and therefore cannot be stored for future retrieval during the treatment planning phase.
Hand-held scanners for in-vivo scanning of dentitions have now become available. One such scanner is described in the PCT Patent Application of OraMetrix, Inc. publication no. WO 01/80761 which is herein incorporated entirely by reference. Because a hand-held scanner allows for scans of the dentition in a relatively short time frame, the scanner can be used to perform an original scan of the patient's dentition. Based on this original scan, an original 3-D virtual model of the patient's dentition can be derived, including a virtual model of each individual tooth. This information is then digitally recorded in some fashion, preferably in a patient record stored in a memory of a scanning node in the scanner system or in an orthodontic workstation.
The scanner becomes an important tool throughout the monitoring treatment process. For example, as the treatment progresses, the movement and position of the teeth can be quantified with a relatively high degree of precision. One way to monitor the movement and position is by performing dentition monitoring scans throughout the various phases of treatment. Monitoring scans, like the original scan, provide a three dimensional virtual image of the dentition, including dental appliances, such as bonded brackets, archwires, and inlays.
Performing monitoring scans provide certain advantages. For example, one such advantage is that monitoring scans allow an orthodontist to discern whether correction in an archwire configuration may be required. For example, during the treatment process, certain biological influences may affect tooth movement. As disclosed in the above-referenced published PCT Application WO 01/80761, treatment planning software can be used to determine whether such corrections need to be made. For example, the treatment planning software on a workstation displays the current situation, and also the target situation. A new customized archwire may be designed on the computer. The relevant information for making the new archwire is sent to a precision appliance service center and a new archwire is fabricated according to revised patient requirements and then shipped to the clinic.
Monitoring scans are also useful to measure and quantify progress while detecting deviations from the expected treatment. Since each of the tooth objects of a current patient's dentition is already stored as a virtual tooth model after completion of an original scan, the monitoring scan need not be of the entire dentition. Rather, during a monitoring scan, the subsequent scanning may need only be of one surface, such as the occlusal surface, or the lingual surface, or alternatively, some combination of the two.
Performing certain monitoring scans after treatment has been initiated, however, often presents certain challenges. For example, for certain scanning technologies utilizing reflected projected patterns such as described in WO 01/80167 to be successful, the scanning requires that the surface of the scanned object allow for good reflectivity in order for the scan to adequately capture the image. There are, however, a number of complications that often arise during a monitoring scan that can often result in obtaining either incomplete or inaccurate three dimensional surface information.
For example, monitoring scans are often result in providing an orthodontist incomplete scan data of the entire dentition. Because of the incomplete nature of certain monitoring scans, the resulting incomplete scan data makes the analysis of the patient's dentition difficult.
In addition, monitoring scans often attempt to acquire accurate and complete scan results of dental devices having small or minute geometrical structures. For example, a monitoring scan often involves scanning pre-positioned bonded brackets. The size of the bracket, and the bracket component parts, also pose problems in obtaining accurate scan data.
For example, FIG. 1A illustrates a typical arrangement of a bracket structure 5 of a bracket bonded to a patient's tooth. As shown in FIG. 1A, the bracket structure 5 comprises a number of straight edge portions 4a, b, c, and d extending out into space in the x, y, and z directions. The bracket also includes an archwire slot 3 having a very narrow width. These portions contain sharp edges as well as certain well defined lines. This bracket arrangement 5 also comprises two bracket wings 1a and 1b. As can be seen from FIG. 1A, these bracket wings 1a,b have a defined length L and a defined width W equal to the length of the slot 3. Obtaining accurate scan data of these types of sharp edges and lines is often difficult since these geometrical structures cause scattering and poor image acquisition. Scattering concerns are even more prevalent where a bracket structure is even more defined, for example, where the bracket structure includes more than two bracket wings.
The size of the bracket also is a concern in obtaining accurate scan data. For example, conventional brackets are often only 3×4×3 mm in size or thereabouts. The small dimension of the bracket, and therefore the bracket component parts (wings, slot, etc.) makes obtaining accurate bracket scan data even more challenging.
These various bracket edges make it difficult to obtain accurate and complete scan information, thereby making it difficult to obtain accurate and complete scan data and therefore construct a 3-D virtual model of the dentition plus brackets. Due to the small size of bracket wings, bracket slots and their related geometries, the size of the bracket structure further causes complications due to the resolution of a projected pattern that may be used in various 3D scanning technologies. For example, where a scanner utilizes a resolution of approximately 0.25 mm, obtaining a complete and accurate scan data from a wing of a bracket will be difficult. For example, wings 1a,b of bracket 5 may only be 0.8 mm. Furthermore, obtaining complete and accurate scan data for the slot 3 will be difficult not only because of the slot width but also because of shadowing issues.
Incomplete and inaccurate scan data makes it difficult to construct an accurate three-dimensional model and thereby determine where the bonded bracket actually resides in three-dimensional space. And, since it is difficult to determine the exact position in 3-D space of the bracket, there will be further difficulty in determining the exact position of the archwire slot, and therefore the required archwire configuration. These scanning inefficiencies may be further prevalent where the dentition is scanned in-vivo, that is, where the object being scanned (dental appliance) is covered with light scattering elements such as water, saliva, or other types of moisture.
Another scanning quality issue that may arise during treatment concerns performing a monitoring scan after a patient's teeth have moved, as a result of the treatment or biological process. For example, the treatment process oftentimes begins with an orthodontist making an original dentition scan of a patient beginning the treatment process and deriving an original three dimensional virtual model of the patient's dentition. As previously described, an original scan will establish an original virtual 3-D model of each tooth without any type of dental appliance previously installed. In such a situation, the complete virtual model would contain an individual virtual tooth model for each tooth, excluding dental appliances. Therefore, the previously described scanning quality concerns relating to either incomplete or inaccurate scan data would not be present.
However, for certain patients, sometime after a first scan is completed and an original three dimensional virtual model has been derived, a bracket placement tray is fabricated. The bracket placement tray enables the brackets to be bonded to the teeth. Some time later, after the bracket tray is fabricated and only after the brackets have been bonded to the dentition, the patient will undergo a monitoring scan. One reason for the monitoring scan is to confirm accurate bracket positioning (i.e., to confirm that the bracket placement tray placed the bracket at the desired location). Because of certain inherent logistical delays, the monitoring scanning process may take place a certain amount of time after the original scan was completed. For example, in certain circumstances, bracket bonding may occur 3 to 5 weeks after the original 3-D virtual model had been obtained. But during this interim 3 to 5 week time period, the teeth may have already shifted. Therefore, the resulting subsequent monitoring scan may confirm that the original virtual 3-D model is no longer correct and must therefore be updated to reflect various new tooth positions.
Consequently, based on such scanning concerns, there is a general need for a scanning method that can accurately locate an object such as an orthodontic appliance having a predetermined geometry in three-dimensional space. This need arises in the context where both complete and incomplete scan data is present. Alternatively, there is a general need for a process that can generate an accurate virtual model of the teeth and the appliance and thereby locate manually bonded brackets. There is a further need to provide a scanning method that compensates for flawed scan data that can oftentimes arise from performing an incomplete scan, particularly where the scan involves scanning a dental appliance. There is also a general need to be able to accurately obtain a three-dimensional detention model including both teeth and a dental appliance, such as bonded brackets. Another need arises where it is generally not possible to scan an object due to restrictions in certain types of scanning technologies (e.g., scan resolutions). There is also a general need to obtain a virtual 3-D tooth model of a patient's entire dentition where the patient's dentition includes a dental appliance, such as bonded brackets.